Process for making leather sheets



Patented Apr. 1, 1941 TENT QFFICE PROCESS FOR '1 I G LEATHER SHEETSThornton L. Lynam, New Bediord,

No Drawing. Application November 11, 1936, Serial No. 110,388

6 Claims. (CI; 92-21) My invention'relates generally to productscontaining leather and to process of making the same, and particularlyto products of this type the principal ingredient of which is ground,torn, shredded or comminuted leather, and to a proces of manufacturingthese products in part on an ordinary paper making machine. Thisapplication is a. continuation in part of my copending application"Leather products and processes of making the same," Serial No. 724,618,filed May 8, 1934.

An important object of my invention is to provide sheet material hi thecharacter indicated having leather as its principal ingredient, the saidsheet being highly absorbent and at the same time relatively dense andopaque in comparison to similar sheets of common absorbent paper beingmanufactured at the present time for imitation leather purposes.

It is also an important object of my invention to provide a process ofmaking products of the character indicated consisting in forming thesame on an ordinary paper making machine and subsequently impregnatingthe products to give the products the desired finish and texture.

It is also an important object of my invention to provide products ofthe character indicated by the method of manufacture stated, which havethe feel, odor, appearance and other characteristics of genuine leatherand are capable of being subsequently impregnated with vulcanizable andunvulcanizable binders and body forming materials.

free from lumps, in any suitable proportions on an ordinary paper makingmachine, whereby to produce an absorbent sheet or body having a smoothsurface, a long fibre, and having the odor, appearance, and feel ofleather, and adapted to be subsequently impregnated with binding machineis susceptible to treatment with rubber cements (having inflammablesolvents) as subsequently described herein.

Absorbent papers mad from alpha, kraft and rope, and of other relatedsubstances have heretofore been made for-conversion into imitationleather bases by impregnation with difierent Another important object ofmy, invention is to provide leather-containing or all-leather sheets ofthe character indicated above which are not subject to air-size.

It is also an important object of my invention to provide in a processof the character indicated above, steps producing vulcanization of theproducts subsequent to impregnation with vulcanizable material, the saidsteps applying eq ly well to products containing only leather'as well asproducts containing other substances as well.

Other objects and advantages of my invention will be apparent from a.reading of the following description and explanation wherein forpurposes of illustration I have set forth preferred embodiments of myinvention.

The present invention contemplates the formation of material of thecharacter indicated in sheet form having an all-leather content oftanned ground leather or a combination of paper types of compounds andcompositions. These papers were usually coated with cellulose com-lpounds, embossed and sold to the trade as a leather substitute. There isnow a great demand for leather substitutes in certain industries,notably 'in the shoe industry, but the presently available substituteslack certain qualities which are inherent in genuine leather, such asflumness, softness, leather odor, feel, appearance and strength. Withthe exception of certain rope reinforced stocks, the presently availableleather substitutes lack useful strength.

Leather substitutes made from paper are objectionably ununiform and aretranslucent and when held up to the light disclose a blotchy web.

The products of the present invention in contrast to those alluded toabove, have all of the desirable leather qualities, and when held up tothe light, no transparency whatever is observable, the formation of theweb being very dense. Despite this dense character the products arehighly'absorbent, and this highly absorbent yet dense character is dueto the type of fibres and treatment used.

It is obvious that the availability of leather substitutes made 01'all-leather fibres or a combination of leather and paper fibres havingthe advantages and desirable characteristics indicated should createanenormous demand for the same, in view of the present lack of anycapable or of any attractive substitute for leather.

The coarse or long fibres used in my process making fibres and tannedground leather fibres, are obtained by selecting the finest of barktannages of shoe sole scrap and, by means of a very intricate mechanicaldevice, so shredding or tearing these fibres that they retain a long,soft, fibrous construction of fibre.

The fine or short fibres used in the present invention are obtained byselecting a different grade of leather from that used in obtaining thelong fibres, such as that used for upper stock and grinding it through adifferent type of intricate mechanical device to produce a uniformlength of soft, absorbent powdery fibre.

It will be understood that the grinding, shredding or tearing of thisleather is no simple matter and must be carried out along definitescientific and mechanical lines with due regard being given to thechemical and physical constitution of these fibres so that they will notbe burned or suffer other injury rendering them unsuitable for thepurpose intended. The actual fact that the long fibres and short fibrescannot be produced on the same machine proves the delicacy of thisoperation and the accuracy necessary for proper results.

It is not possible to use ordinary scrap for the purposes of the presentinvention because such scrap contains large quantities of impuritiessuch as sand and emery dust, and leather dust from a variety ofdifferent tannages and different c01- ored leathers, so it is obviousthat very special attention must be given to selecting and producing theproper kinds of disintegrated leather to be used if a satisfactory sheetis to be produced.

- Ordinary scrap could be made into a sheet by screening out theundesirable parts but this would produce only an unsatisfactory sheetlacking uniformity, because of the different varieties of tannages used,and the other impurities referred to which it contains. Ordinary scrapconsists principally of leather dust secured by sanding or buifingvarious kinds of leather.

The available physical characteristics and dimensions of the coarse andof the fine leather fibres are as follows:

The results of an analysis of a sample of the fine short fibres were asfollows:

Per cent Material passed through a 20 mesh screen;

that is, a wire screen having 20 openings per inch By weight failed topass a 28 mesh screen Passed the 28 mesh screen but was retained on the40 mesh 3.4 Passed the 40 mesh screen; retained on the 50 mesh 5.1Passed the 50 mesh; retained on 80 mesh 7.3 Passed the 80 mesh; retainedon 200 mesh- 8.8 Passed through the 200 mesh screen 44.7

The various fractions separated in this way were found to diiferconsiderably in their appearance under the microscope.

The material which was retained on the 28 mesh screen consistedpractically entirely of fibers of fairly uniform diameter, namely, about0.004 to 0.008 millimeter. These fibers varied somewhat in length, butwere mostly 0.8 and 1.6 millimeters in length. There were also in thisfraction a number of loose aggregates or bundles of fibers, as well as anumber of very fine fibers or fibrils.

The fraction passing the 50 mesh screen and left on the so mesh-screenconsisted c efly of clumps of very short fibers of about the samediameter as above, but having an average approximate length between.0.2and 0.6 millimeter as nearly as'they'could be measured.

The fraction passing the 80 mesh screen and retained on the 100 meshconsisted of fibers together with a considerable proportion of smallpieces of skin tissue of widely varying shape and size, but mostly,roughly two or three times longer than the width. the largest diameteraveraging between 0.2 and 0.4 millimeter.

The fraction passing through the 200 mesh screen, which constitutedalmost one-half of the material by weight is chiefly fine dust, which isapparently composed of bits of skin tissue, very short fiber fragments,etc. They are mostly, approximately round or oval in shape. The largestparticles may be about 0.1 millimeter in their largest dimension, whilethe great majority of the particles appear to be between 0.03 and 0.05

- millimeter in their largest diameter.

Turning to the coarse material, it was found impossible to subject thisto a screen analysis owing to the readiness with which this materialforms into flocks or balls of fiber.-

As far as could be judged this sample consists almost entirely offibers, although there appears to be a small amount of very short fibersand dust. The length of fibers varies over a very wire range, butapparently most of them are of the order of several millimeters inlength. If

the fiber is opened or picked apart by hand it is possible to shake outa number of short fibers,

and we have found some material which will pass even a 200 mesh screen.A determination of the verage fiber length or the distribution ofparicle size in this sample would be extremely difilcult.

The two samples differ also in their bulk density, by which we mean thevolume occupied by a given weightof the material. The fine sample whenloosely packed has a bulk density of 12.3 pounds per. cubic foot, whilethe coarse sample under the same conditions weighs 6.1 lbs. per cubicfoot. It is, therefore, evident that the fine sample is almost exactlytwice as dense as the coarse. Other experiments in which the materialswere packed under. higher pressure indicated almost exactly the samerelation between the two samples.

The dry bark: tanned shoe sole scrap is selected and put into thedisintegrating machine which is equipped with a special shredding rolland tearing device which both shreds and tears, leaving the fibres longand silky and of a very uniform length. It is, of course, impossible todisintegrate leather without some useless matter being present so thestodk is first screened to take out the coarse untouched hubs and isthen put through a metal shaft consisting of baiiles with a forceddraft, which takes out even the finest unshredded particles and leavesthe. re-

sultant fibres perfectly clean and ready to be used as a constituent ofa leather sheet in accordance with the present invention.

The upper stock leather is selected for proper tannage colorandcondition and is then ground 7 in dry form througha special grindingapparatus, which grinds .without burning the tender leather fibres, andis then screened and put through the baiifes for cleaning out the finenubs. After going-through these-baiiles, it is then ready to be used asa constituent of leather sheet in accordance with the present invention.

Beaten fibres utilized prior to the present inwhere it becomesnon-absorbent, so that where it the leather fibres -is onlyapproximately three-quarters of an hour vention are those fibres thatare beaten in wet form in a mechanical beater. Veryflittle atten tion isgiven to what type of leather fibres is used and' they are seldomselected. But. assuming thatthe same stock as used in the presentinvention was selected for beating purposes it is evident that thefibres must be disintegrated in the wet form before they could be runinto a sheet v with or without a mixture of other fibres. The beating ofthese wet fibres to a point where'they would be suitable to run on apaper making ma chine would, undoubtedly, take about 12 hours ifeverything wentv well, but in order to thoroughly eliminate the nubsthat. resist disintegration it might take 24 hours to eliminate themsufilciei'itly so that a run could be made. Even then this -beaten stockwould still contain imperfectly beaten nubs that could cause lumps andspecks in the sheet to the extent that it might become necessary to sandthe surface to eliminatethe'se nubs. The beaten fibres being wet theycould not be screened or put through forced draft to remove nubs andother impurities. Considering the above description of the beatermethodand the difilculties surrounding this method including the timerequired for disintegration by beating and the fact that only animperfect result is possible by the beaten method, it is evident that alot of work must be done to secure an imperfect job.

Beating a lot .of leather for 12 hours has a tendency to hydrate theleather to the point is necessary to beat it for 24 hours the result isobvious; so that as a matter of fact, an absorbent sheet cannot beobtained where the fibres are beaten in a mechanical heater for suchperiods of time.

The properly ground, torn or shredded fibres of the present invention donot require any beating, 40 so that they retain their absorbency and allthat is necessary to produce an absorbent sheet from these all-leatherfibres orfrom a combination of these leather fibresand paper makingfibres is to simply mix the fibres together in a mixer with water. so asto get a uniform distribution of leather fibres throughout the slurry ormix, Jorden, and then to run the sheet on the paper making machine. Thetime required for mixing with the paper making fibres as against twelvehours upwards in the case of processes involving beating the leather.

The torn, ground, or shredded fibres, of the present invention containno bothersome or unground nubs, the whole fibre structure-being uniform.Therefore, whether run'as 100%.leather fibres or as a combination ofleather fibres and paper making fibres, the sheet is absolutely freefrom lumps. The beating referred'to above is a mo long drawn out processbesides destroying'the absorbency, and is unreliable at best, whereasthe previously ground, shredded or torn fibres of the present inventionare ready for instant use, andv they have full saturating qualities andproduce a very reliable and uniform sheet. Experience in the manufactureof these leather sheets, shows that the best'coarse tanned leather 1fibres forproducing asheet-isbbtalned by tearing and shredding selectedbark tanned shoe sole scrap. In manufacturing a. sheet where the finelyground or coinminuted leather is used, certain types of tanned upperstock are found best.

In both cases, the. shredding, tearing or grinding methodsdescribedabove produce fibres entirely leather fibres are beat-en ordisintegrated inthe beater wet and a leather sheet whose dry fibres arepreviously ground, torn, shredded or comminuted and required no beatingor further disintegration to produce the sheet.

Heretofore, no ground,'torn, shredded or comminuted leather has beenavailable for manufacturing. a sheet of the type as disclosed in thisapplication. Not only are the ground, torn, shredded or comminutedleather fibres distinctly advantageous in the manufacture ofa sheet, butthe fibres, taken together with the method of manufacture. produce asheet far superior and without parallel for saturating purposes.

No leather sheet, no matter how well made or by the method of heating itin the beater while wet from the raw stock unground could possiblyproduce a sheet that would in any way compare with my idea because itwould not be capable of being saturated, and without having saturatingqualities it is absolutely worthless as a substitute for leather.

It shouldalso be noted that the sheet is made without any type ofbinding material whatsoever. It contains nothing but the leather fibresthemselves, and because of the fact that no binding material of anydescription is used during the actual manufacture of the sheet itself,it is apparent that there is nothing contained in the sheet at thisstage to prevent saturation thereof and that a sheet made in accordancewith the -follo "ingrdescribed methods, is quite absorbent and capableof being impregnated with numerous kinds of materials. To put itplainly, this sheet is made without binder and is subsequentlyimpregnated with'binders.

Following the disintegration operation, the tanned leather fibreswhether of coarse texture or of finely ground texture are ready to usein the formation of either a leather fibre sheet or in conjunction withpaper making fibres.

For instance, if it is desired to' produce a sheet consisting of 100%leather fibres, 500 gallons (4250 1bs.) of water is run into a mixer, towhich is added an alkaline solution which has been previously dissolvedin some warm water. The object of adding this alkaline solution is toelimihate the natural oils and greases which the leather contains. Thealkaline solution having been added to the 500 gallons of water, I thenadd 600 lbs (dry weight) of the previously ground,

torn, shredded or comminuted tanned leather fibres which have beenpreviously soaked in water while in the bags. As soon as these 600 lbs.(dry weight) of the previously soaked leather fibres are put into themixer containing the 500 gallons.

of water, and mixed, a test is made to determine the pH reading. Thisshould not exceed 5.5 because the leather paper will ot permit ofsaturation if it is on or near the pH is over 5.5, an acid is added, forinstance, vitriol to bring the pH to between 4.5 and 5.5. About onequartof the above acid in ten quarts of water is required to be added tothe above described quantity of leather fibres if the pH should happento read over 6 to 6.5.

Now having established the pH reading, su'fil-.

cient water is added to-bring this slurry toss,

workable condition-for example, 96 water alkaline side. If the v and tiof tanned leather fibres. The proportion of alkaline solution dependsupon the type and condition of the ground, torn, shredded or comminutedleather used, but for general purposes fi; of 1% to 1% of the alkalinesolution is used based upon the pounds of water and pounds of leatherinvolved. It has been found under actual manufacturing conditions thatan alkaline solution of material known as Alkanol B which is the sodiumsalt of naphthalene sulphonic acid derivative, can be used to the bestadvantage. It is a cream colored powder which is readily soluble in warmor hot water. It is very soluble in alcohol and acetone but is'insolublein most other organic solvents. It is an extremely em-.

cient wetting agent in concentrations as low as 1 6% and as high as 1%and will wet all fibres and surfaces practically instantaneously.Alkanol B has no detergent eifect except as it acts as an emulsifyingagent for solvents and detergents. Such alkaline solutions as causticsoda, soda ash or other alkalies can be used but the use of "Alkanol Bworks out considerably cheaper and more effectiveb'.

While the alkaline solution is necessary for the removal of oils andgreases contained in the leather, it has been found that the leatherpaper must be on the acid side to afford proper absorption. Therefore,it is very important that the pulp or slurry should have the proper pHreading .before it is run on the paper making machine.

The theory of the action of alkaline wetting-out I but furthermore theyallow the production of a leather paper that does not subsequently airsize. In other words, they permit of the manufacture of a leatherproduct which will retain its absorbent properties over a long period oftime which is really the most important point of all.

The leather fibres having been wet and having had the oils and greaseremoved through the use of the alkaline solution and having beenacidified to the proper pH reading of 5.5 and water havin been added sothat the slurry contains about 96 of water and il of tanned leatherfibres, the slurry is thoroughly and continuously mixed until ahomogeneous mass is obtained. This takes approximately a half hour,after which the slurry is pumped through a Jordan or refiner for thespecific purpose of refining the fibres so as to obtain a betterformation on the paper making machine. making machine through screens toremove impurities such as dirt and strings which may have become mixedwith the fibres during the preparation of the same.

The stock then fiows onto the endless wire of the regular paper makingmachine (whether Fourdrinier or cylinder). Here a large proportion ofthe water is drained ofi by gravity and suction and the web then formedas it leaves the-endless wire of the regular paper making machine but isnot "wet pressed as is a regular paper but allowed to pass directly tothe paper making dryers. The elimination of "wet pressing insures asofter, more absorbent, bulkier type ofsheet.

It should be observed that when making a sheet consisting of 100% tannedleather fibres that the heat of the drying cans should not exceed 150They are .then pumped to the paper of the mixed paper making fibres.

burning the tender leather fibres while they are being dried around thecans. After being dried around the cans, the sheet goes to the calenderwhere it is run through a sumcient number of rolls to soften and smoothup the surface and give it the proper thickness, after which it is slitand wound on a' core in whatever width may be required.

There has been no mention of binder because here no binder is used inthe formation of the slurry nor is there any spraying of rubber or useof coagulant during the manufacture of the sheet. The slurry is runexactly like paper with the exceptions noted.

Leather and paper making fibre sheet The manufacture of a sheetconsisting of previously ground, torn, shredded or comminuted tannedleather fibres and paper making fibres is quite simple.

Assuming the manufacture of a sheet consisting of 80% paper makingfibres (10% Manila rope fibres and 50% wood pulp "sulphate fibres) and40% previously tannedieather fibres, I proceed as follows: I

Both fibres are cookedseparately, the rope fibres requiring a differenttreatment from the wood pulp fibres. After being cooked these fibres aremixed together in the proportion of 600 gallons of water andapproximating 720 lbs. (dry weight) The or 720 lbs. (dry weight) of.mixed paper making fibres are strongly alkaline. The object of mixingthem together isto determine their pH reading and to thoroughlycommingle them. These paper making fibres are now washed in clear wateruntil the pH reading is 10 and-the mixer is then stopped.

In the meantime, 40% or 480 lbs. (dry weight) of the previously ground,torn, shredded or come minuted tanned leather fibres which have beenpreviously soaked in water overnight in the bags are prepared asfollows:

400 gallons of water are runinto a mixer to which is added 1% of 1% andas high as s of 1% of the alkaline solution (in this instance Alkanol B)which has been previously dissolved in a small amount of warm water. Themixer is then run continuously-for about ten minutes to thor- .oughlymingle the water and the alkaline substance. Now the 480 lbs. (dryweight) of ground,

torn, shredded or comminuted tanned leather oughly mixed as describedabove, are added to 60 the tanned leather fibres in the mixer and themixer is run again for a period of approximately twenty minutes tothoroughly amalgamate the paper making fibres with the tanned leatherfibres. At this time a test is made to determine the pH reading. If thepH reading is over 5.5, an acid is added, for example, vitriol to bringthe pH reading between 4.5 and 5.5. Different amounts of acids arenecessary for each batch because leathers difier. However, about onequart of acid in ten quarts of water will sufilce as an illustration.No'w having established the pH readins, sufiicient water is added tobring this pulp or slurry to a workable condition, such as 96%% waterand 355% mixed tanned leather and paper degrees Fahrenheit because ofthe liability of making fibres.

- up the surface and give it the after which it is slit and wound on acore of 'with the exceptions noted.

While the alkaline treatment as applied to the tanned leather fibres andthe paper making fibres is necessary to remove oils, greases, ligninsand the like, it has been found that this combination of papermaking-and tanned leather fibres must be on the acid side to produceproper absorption, therefore, the addition of vitriol above referred to.It isvery important that the pulp or slurry should have the proper pH-reading, namely, approximately from 4.5 to 5.5 in order that it may berun successfully on the paper making machine and have proper absorptionqualities.

The alkaline solution acts also as a wetting-- out agent and serves tobreak down surface tension as well as dissolve the oils, greases,llgnins and the like and permits better penetration of liquids andfurthermore, it permit the production 01' a sheet consisting ofpreviously ground, shredded, torn or comminuted leather fibres and papermaking fibres which does not subsequently refining the fibres so as toobtain a better formation on the paper making machine, and it is thenpumped to the paper making machine through screens acting to removeimpurities such as dirt and strings which may have become mixed with thefibres during the preparation of the same.

The stock fiows onto an endless wire of the regular paper making machine(whether Fourdrinier or cylinder). Here a large proportion of the wateris drained oil by gravity and suction but the web thus formed as itleaves the "endless wire of the regular paper making machine is not "wetpressed as is ordinary paper but it isallowed to pass directly to thepaper making dryers. The elimination of; wet pressing" insures a softer,more absorbent and bulkier type of sheet. It is not necessary to observethe same conditions as to heat as when making a sheet of 100% tannedleather fibres because the paper making fibres do not char as do thetender leather fibres and these paper making fibres act as an insulatorand prevent the heat in the cans from burning the tender leather fibres.

After being dried around the cans, the sheet goes to the calender whereit is run through a sufiicient number 01' rolls to soften it and smoothproper thickness,

whatever width may be required.

7 It is to be noted that here as in the case of 100% tanned leatherfibre sheet no binder'is used in the formation of the slurry and nospraying of rubber or any other binder takes place and that no use ofcoagulant or fillers attends the manu-' facture of the sheet. It is runexactly like paper It'should also tie noted that .when a sheet is madein accordance with the above processes described herein whether of 100%previously ground tanned leather fibres or of a combination of.preyiously ground. tanned leather fibres and paper making fibres, it canbe kept in storage indefinitely and will still be capable of beingimpregnated as easily and perfectly as when freshly made. The method ofmaking either or both of these sheets provides for the removal andelimination of oils, greases, lignins and other resinous substanceswhose tendency it is to prevent saturation, but this is not necessary inall cases.

Having succeeded in making the two types of sheets commercially inaccordance with the above descriptions, 'each of these sheets is readyfor impregnation, neither having been up to this point in any wayaltered by any impregnation, spraying or containing any binder orfilling materials whatsoever.

To make an absorbent sheet is one thing and to impregnate it is another.The above described sheet made without binder is very absorbent and canbe made in any desired width of roll or thickness of sheet from .010 to.070 of an inch thick, any thickness of which can be impregnated at anytime. The difference between this sheet and sheets covered byprior-processes is that the end achieved here is to make an absorbentsheet from previously ground, torn, shredded, or comminuted unbeatentanned leather fibres or previously ground, torn, shredded, orcomminutedunbeaten tanned leather fibres in combination with paper making fibresthat can be carried in stock as long as required and can be impregnatedat any time, due to the fact that it does not air size. When it comesoff the machine it is not impreghated but can be impregnated at any timeto such paper making fibres as cotton,

meet current needs with any impregnating com-- pound to make differenttypes of products. The non-impregnated material is. not cut up. intosheets. It is carried in rolls of various yardages up to 2000- yardsaccording to thickness, so that when it needs to be impregnated for someparticular purpose it can be very effectively handled.

If, however, it is desired to make a leather paper containing othersubstances besides leather,

in addition to the hemp rope and wood pulp (sulphate) paper makingfibres before mentioned,

rayon, rags,

' jute, sisal, long wood, Chinese or Oriental grass,

, is added to them in whatever or asbestos fibres may be employed. Thesepaper making fibres are cooked and otherwise treated to procure maximumabsorbency and are either added to the disintegrated leather or theleather proportions areconsidered proper to produce sheets 01' a givencharacter.

Having made the above mentioned sheet free from binder with 40% leatherfibres and 60% of paper making fibres, the

done as follows:

impregnation of same is Without regard to the kind of impregnatingmaterials used, the manner of impregnating and drying is substantiallyas follows:

A saturating machine being provided, a roll 01' all leather or combinedleather and paper stock it moves along and the surplus is squeezed outsheeting is placed upon the unwind stand and is then unrolled andimmersed in the impregnating material in the tankand the surplussqueezed out between squeeze rolls or it is allowed to float upon thesurface of the impregnating material as with squeeze rolls or it ispassed between two rollers containing a. puddle of the impregnatingmaterial, which not only impregnate but squeeze out -the surplusimpregnating material. The sheeting then goes through the drying systemcontaining usually a festoon, straight pass dryer, can dryer, steamcoils or combination of same,

in continuously circulated hot air wherein the moisture is entirelydried out of the stock, which has just been impregnated. After it isdry, the impregnated sheeting is rolled into a bundle on an ordinaryreeling machine and is then ready for the next step, whether it becombining, finishing, embossing or any handling which may be dictate'dby the purpose for which it is to be used.

The impregnating compound usually consists of some combination of eitherlatex, Vultex," rubber cement, dispersed rubber, or vulcanizable latexwith some gum adhesive element such as one or more of those describedabove. It is the amount of solids which is left in the impregnatedproducts which determine the quality thereof. It is possible to use aslittle as 2% of rubber and 98% of adhesive substance, and it is possibleto obtain sheeting containing as much as 70% of solids.

The amounts of rubber and adhesive substance to be used will varyaccording to the results desired.

For instance, if a very firm rigid material is desired I impregnate thesheeting with a solution consisting of 14 gallons of rubber and 20 -ardrubber millers, for softeners, and the resultants are then'dissolvedwith the aid of gasoline, benzol or similar solvents in an agitatoruntil a smooth heavy solution is obtained having the desired rubbercontent.

The method of impregnating the sheeting with such a rubber impregnatingsolution is as follows:

The roll of sheeting to be so impregnated is placed on the unwindingframe of the saturating machine'and passedeither through the solution ina tank or floated 'on the surface of the solution until thoroughlysaturated and is then squeezed between rolls to remove the surplussolution; or passed through squeeze rolls where a heavy solution isthrown on the top side of the sheeting just before it goes through therolls.

The passage of the sheeting through the squeeze canizing elements, theexcess squeezed out and then passed through a dryer to dry out orevaporate the solvents after which it is passed through another enclosedcompartment at slow speed where the temperature may run from 220 to 250degrees Fahrenheit and there remain in the compartment exposed to theabove heat for a period of from one'to two hours. It is advantageous tohave a current of air in the compartment and to have the stock passthrough in continuous movement. An enclosed festoon is preferred, butother types of dryers can be utilized, for this work because the heatsand speeds can be regulated to meet variable conditions.

It is to be understood that reference herein to combination of leatherand paper fibres in the form of sheets is not intended to apply towovenfabrics and the like, but to include only either the be definitelyunderstood that I do not desire to rolls causes the solution to besqueezed into the sheeting and the surplus solution to be squeezed out.

The thus impregnated sheeting is then passed through the festoon dryeror passed through a straight pass or other type of dryer to pass off thevapors. The resultant sheeting is then vulcanized on both sides byexposing both sides of theimpregnated sheet to the action of vapors ofsulphur monochloride in a vulcanizing chamber ac- .companied by aircirculation and heat operating limit the application of the inventionthereto, and any change or changes may be made in the materials and inthe manner of assembling the same,

within the spirit of the invention. and the scope of the subjoinedclaims.

What is claimed is:

1. A method of making an unsized binder-free permanently absorbentleather-containing sheet capable of subsequent impregnation, said methodcomprising providing a quantity of fibres, a portion of said fibresbeing short, fine unhydrated leather fibres obtained by dry grindingtanned, scrap leather and another portion of said fibres being long,coarse unhydrated leather fibres obtained by dry shredding tanned scrapleather, then mixing said fibres with water to obtain auniform'distribution of the fibres in the resulting slurry, thenadjusting the pH of the slurry to between 4.5 and 5.5, and then runningsaid slurry on a paper making machine to form a sheet,

2. A method of making an unsized binder-free permanently absorbentleather-containing sheet capable of subsequent impregnation, said methodcomprising providing a quantity of fibres, a portion of said fibresbeing short, fine unhydrated leather fibres' obtained by dry' rindingtanned scrap leather and another portion of said fibres being long,coarse unhydrated leather fibres obtained by dry shredding tanned scrapleather and another portion of said fibres bei g P per making fibres,then mixing said fibres with water to obtain a uniform distributionof'the fibres in the resultingslurry, then adjusting the pH of theslurry to between 4.5 and 5.5, and then running said slurry on a papermaking machine to form a sheet.

3. A method of making an unsized binder-free permanently absorbentleather-containing sheet capable of subsequent impregnation, said methodcomprising providing a quantity of fibres, all of said fibres beingunhydrated leather fibres obtained by dry grinding tanned scrap leather,then mixing said fibres with water containing an alkaline wetting agentfor approximately three-- quarters of an hour assuring definitesubsequent absorptiveness while obtaining a uniform distribution of thefibres in the resulting slurry, then consistency, and then running saidslurry on a paper making machine to'fonn a sheet.

4. A method of making an imitation leather sheet, said method comprisingproviding a quantity of fibres, a portion of said fibres being short,fine unhydrated leather fibres obtained by dry grinding tanned scrapleather, another portion of said fibres being long, coarse unhydratedleather fibres obtained by dry shredding tanned scrap leather, thenmixing said fibres with water to obtain a uniform distribution of thefibres in the resulting slurry, then adjusting the pH of the slurry tobetween 4.5 and 5.5, then running the slurry on a paper making machineto form a sheet, and thereafter impregnating said sheet with at leastone of a group consisting of dispersed rubber, dispersed rubber withwater soluble gum, dispersed rubber with natural resinous emulsions,dispersed rubber with synthetic resinous emulsions produced by theaction of ammonia upon resinous bases.

5. A method of making an imitation leather sheet, said method comprisingproviding a quantity of fibres, a portion of said fibres being short,fine unhydrated leather fibres obtained by dry grinding tanned scrapleather, another portion of said fibres being long, coarse unhydrated.

leather fibres obtained by dry shredding tanned scrap leather, andanother portion of said fibres being cooked paper making fibres mixedwith water and having a pH approximating 10; mixing the leather fibreswith water containing an alkaline wetting agent to obtain a uniformdistribution of the leather fibres in the resulting slurry; then to thisslurry adding the batch of paper making fibres with mixing to obtainamalgamation of the leather fibres and the paper making fibres; thenadjusting the pH of resultant slurry to between 4.5 and 5.5, thendiluting the slurry to a paper making consistency, and then running theslurry on a paper making machine to form'a sheet.

6. A method of making an imitation leather sheet, said methodcomprisingproviding a quantity of fibres, a portion of said fibres being short,

slurry adding the batch of paper making fibres with mixing to obtainamalgamation of the leather fibres and the paper making fibres; thenadjusting the pH of the resultant slurry to between 4.5 and 5.5, thendiluting the slurry to a paper making consistency, and then running theslurry on a paper making machine to form a sheet, then subsequentlyimpregnating the sheet with rubber.

THORNTON L. LYNAIVL-

